Optimization of extraction process of antioxidant compounds from yellow onion skin and their use in functional bread production

Abstract

The major aim of this research was to demonstrate a possible use of antioxidant compounds isolated from onion skin in functional bread production. The scope of the research included a study on the extraction process of antioxidant compounds from onion skin and determination of optimal process conditions using response surface methodology, as well as the investigation of antioxidant properties of bread enriched with onion skin extract. Research showed that total yield of extraction of antioxidant compounds from onion skin using methanol as a solvent was dependent on the applied process conditions i.e. temperature and process time, as well as the ratio of onion skin mass to methanol volume. From 1 g sample of onion skin, the highest yield is achieved at 145 min of process time under 44 °C, using 30 mL of methanol. The obtained onion skin extract was characterized by high antioxidant activity (441.4–593.9 mg QE g−1) which was shaped by high concentration of flavonoid compounds i.e. quercetin (315.6 mg g−1), quercetin-3-glucoside (40.3 mg g−1), isoramnethin (14.8 mg g−1) and kaempferol (10.9 mg g−1). Furthermore, it was found that antioxidant activity of wheat bread enriched with onion skin extract was closely correlated with extract dose.